Acute or plastic changes in brain function can be safely induced in humans by low-intensity electrical stimulation through scalp electrodes. Such electrical stimulation is known as neurocranial electrostimulation (NCS). These changes can be potentially used for therapeutic or performance enhancing applications.
Current technology generally uses stimulation through pairs of large sponge-like electrodes. Transcranial electrical stimulation conventionally refers to short-duration (50-500 μs) of supra-threshold pulses (100-1200 V). Cranial electrotherapy stimulation (CES) utilizes a range of waveforms with peak current levels ranging from 50 μA to 5 mA. Supra-threshold current pulse trains (about 0.9 A) are generally used during electroconvulsive therapy (ECT). DC waveforms normally ranging from 260 μA to 2 mA are used for transcranial direct current stimulation (tDCS). In this document, term NCS is used in a broader sense to include any stimulation using an electrode on the head or cranium.
In some cases, anodal stimulation enhances excitability, whereas cathodal stimulation reduces excitability as has been shown in several studies. Stimulation given to M1 can facilitate implicit learning and TES over the occiptal cortex can facilitate visuo-motor learning. Stimulation has also been shown to alter excitability or resulting behavioral performance in somatosensory and frontopolar cortices. Cranial stimulation is being explored as a non-invasive therapeutic option for the treatment of neurological and psychiatric disorders including depression, stroke, Alzheimer's, and learning disorders. A critical limitation for cranial stimulation efficacy and safety is derived from the need for accurate control of exactly where in the brain the stimulation actually modulates the neuronal activity. TES, and analogous Transcranial Direct Current Stimulation (“tDCS”), are considered to be poorly focused using common “remote bipolar” electrode configuration.
It is therefore an object of the present invention to provide a stimulation system which can accurately target brain modulation.
It is another object of the present invention to provide a stimulation system whose design and application benefits from insights derived from biophysical studies in order to better functionally target specific areas of the brain for more accurate electrostimulation.
It is a further object of the present invention to provide a system which enables more effective and safer cranial stimulation with accurate control of what part of the brain is stimulated for modulating neuronal activity.